Answer:
5/7 is the largest
Explanation:
is the largest fraction because it is the closest to the denominator 7. Think of it as a pizza that for some reason is cut into seven pieces, if you ate 5 pieces you ate most of the pizza. However if you cut this pizza into 12 slices and only ate 2 well you almost didn't eat much and you can continue this idea of pizza for 15/40 and 8/20.
You can also divide these numbers to see the fraction as decimals but it's not necessary.